The present invention relates generally to auditory prostheses and, more particularly, to auditory prostheses for use in the external ear canal.
Many individuals have suffered and currently do suffer from tinnitus. Tinnitus, simply defined, is the perception of sound in the ear which does not, in fact, exist, i. e., is not present in the external environment. These sounds typically may be characterized as a ringing, whistling, roaring or buzzing. Tinnitus has been reported to affect up to thirty percent (30%) of the United States population. Individuals with tinnitus may have symptoms ranging from mild to severe and ranging from chronic to intermittent. Several million people in the United States suffer debilitating tinnitus which interferes with everyday activities. In some cases, tinnitus can be chronic and severe, debilitating the individual.
Several attempts have been made in the past to mask or "cure" tinnitus. Some of these attempts have involved treating the tinnitus by the administration of drugs. An example of these attempts is disclosed in U.S. Pat. No. 4,735,968, Guth.
In some cases the tinnitus is so severe that drastic steps have been taken to eliminate the sensation. The symptom of tinnitus can be "cured" by a section of the VIIIth nerve in one ear, completely eliminating any sensation of hearing in that ear. An example of a drastic attempt to "cure" tinnitus is disclosed in U.S. Pat. No. 4,408,602, Nakajima.
Some prior attempts for suppressing tinnitus have involved the use of electrical stimulation.
An example of this type of electrical stimulation is described in the ATA Newsletter, Vol. 10, No. 1, American Tinnitus Association, pp. 1-4 (March 1985). Electrical stimulation, however does not actually suppress tinnitus but rather simply attempts to mask the existing tinnitus sound with another sound created by the electrical stimulus signal. The ultimate goal of electrical stimulation is to suppress tinnitus without adding any other sounds. In some cases this is possible with direct current (DC) electrical stimulation. However, direct electrical currents cause damage to biological tissue and thus, this method cannot be practiced chronically. In some other cases, the electrical stimulation adds, rather than subtracts, from the sound environment, but for some individuals this may be more pleasant than doing nothing since the tinnitus sound may be so disturbing.
A similar example of masking, in this case with acoustic stimulation is shown in U.S. Pat. No. 4,222,393, Hocks et al, Tinnitus Masker, which discloses a system in which a tinnitus patient is subjected to external sounds of differing pitches to determine the frequency of the perceived tinnitus sound and then provided with signals both above and below the determined frequency in order to mask the tinnitus. These systems do not eliminate or cure the tinnitus but merely superimpose another stimulus on top of the existing tinnitus sensation in an attempt to mask the perceived sensation.
In an article by B. Densert and O. Densert, "Overpressure in Treatment of Meniere's Disease", 92 Laryngoscope pp. 1285-1292 (November 1972), the Denserts described tests they conducted on patients suffering from Meniere's disease. It is to be pointed out that Meniere's Disease, sometimes referred to as cochlear hydrops, is a significantly different condition from tinnitus which accompanies a typical high frequency hearing loss. That is, Meniere's Disease tinnitus represents only a small portion of the tinnitus which exists in the general population. In some of the tests, they conducted local overpressure tests on the middle ear using a tube inserted through the tympanic membrane. In their tests they used a pressure increase upon which a low frequency sine wave was imposed. They require the sine wave oscillating pressure. The Denserts' main intention appears to be to treat patients with Meniere's disease. Since the main symptoms of Meniere's disease are hearing deficiency and vertigo, these are the symptoms which the Denserts have tested. In the question and answer period at the end of the presentation which resulted in this paper, in response to a question, they did say that they had had success in treating the tinnitus symptom.
Densert et al, in PCT International Published Patent Application No. WO 83/02556, An Apparatus for Influencing the Hydrodynamic System in the Inner of an Ear, describes an apparatus for treating Meniere's disease, which has primary symptoms of hearing deficiency and vertigo, with tinnitus being a secondary symptom. The apparatus is a large, stationary, office apparatus which, at certain treatment intervals, attempts to reduce the volume of the endolymph by introducing a fluctuating pressure upon the perilymphatic fluid. It is fundamental in the design of the apparatus that a patient would go to an office, be temporarily connected to the apparatus, undergo treatment and leave the office with the expectation that the changes in the endolymph would remain for a significant period of time. The pressures induced upon the perilymphatic fluid, in order to force a reduction in the volume of the endolymph, requires generating a static positive pressure level (during the treatment time period only) and generating a varying pressure level on top of the static positive pressure. The frequency of the varying pressure is described to be between 3 and 6 Hertz. Thus, the apparatus described in Densert et al PCT attempts to reduce the volume of the endolymph by temporarily inducing a fluctuating positive pressure on the endolymph in order to reduce the symptoms of Meniere's disease which have primary symptoms of hearing loss and vertigo and a secondary symptom of tinnitus.
European Patent Publication No. 0 266 474 A1, of Application No. 8650390.5, Procedure and Equipment for Treatment of Meniere's Disease, also by the Denserts, describes a very similar device. The apparatus requires the generation and transmission of complex pressure pulses in the fluid system of the inner ear in order to reduce the volume of the endolymph. As in the previous publications from the Denserts, a fluctuating, varying, or complex positive pressure is introduced to the inner ear in order to force fluid from the endolymph for the treatment of Meniere's disease, i. e., cochlear hydrops.